Regulatory conditions in the automotive market have led to an increasing demand to improve fuel economy and reduce emissions in current vehicles. These regulatory conditions must be balanced with the demands of a consumer for high performance and quick response from a vehicle. Variable displacement internal combustion engines (ICEs) provide for improved fuel economy and torque on demand by operating on the principal of cylinder deactivation. During operating conditions that require high output torque, every cylinder of a variable displacement ICE is supplied with fuel and air (also spark, in the case of a gasoline ICE) to provide torque for the ICE. During operating conditions at low speed, low load, and/or other inefficient conditions for a fully displaced ICE, cylinders may be deactivated to improve fuel economy for the variable displacement ICE and vehicle. For example, in the operation of a vehicle equipped with an eight cylinder variable displacement ICE, fuel economy will be improved if the ICE is operated with only four cylinders during low torque operating conditions by reducing throttling losses. Throttling losses, also known as pumping losses, are the extra work that an ICE must perform when the air filling the cylinder is restricted by a throttle plate during partial loads. The ICE must therefore pump air from the relatively low pressure of an intake manifold through the cylinders and out to the atmosphere. The cylinders that are deactivated will not allow air flow through their intake and exhaust valves, reducing pumping losses by allowing the active cylinders to operate at a higher intake manifold pressure.
In past variable displacement ICEs, the switching or cycling between the partial displacement mode and the full displacement mode was problematic. Frequent cycling between the two operating modes negates fuel economy benefits and affects the driveability of a vehicle having a variable displacement ICE. The operator's driving habits will affect the number of times a variable displacement ICE will cycle between the partial and the full displacement operating modes, and the fuel economy benefits of a variable displacement ICE. Frequent cycling will also impact component life in a variable displacement ICE.